In a medium saucepan, bring 2 cups water to a boil with the rice, grated garlic and 1/2 tsp. each salt and pepper. Lower the heat, partially cover and simmer for 25 minutes.
Meanwhile, in a dutch oven, heat the EVOO over medium-high heat. Add the shopped sausage and cook for 1 minute. Add 2 tbsp. water, the sliced garlic, the scallion whites, bell peppers and celery. Lower the heat to medium-low, cover and cook, stirring occasionally, until the vegetables are softened, about 8 minutes. Add the chopped tomatoes and cook, uncovered, until the tomatoes release their juices, about 3 minutes. Stir in the parcooked rice. Bring to a simmer, then cover and cook over low heat, stirring, until the rice is tender, about 10 minutes.
Stir in the sliced sausage, the shrimp and quartered tomatoes; add 1/4 cup water (or more) if the pot is dry. Cover and cook over low heat until the sausage is heated through and the shrimp are opaque, about 5 minutes. Sprinkle the scallion greens on top.